The present invention relates generally to the field of content communication and more specifically to a system for communicating video content on demand through a communication network having a communication protocol with callback time.
Conventional systems for delivering video content on demand to subscribers are becoming well known. VOD (video on demand) is an interactive service in which content (e.g., video) is delivered to a subscriber over a point-to-point network (e.g., a cable system) on an on demand basis. A subscriber may order and receive programming content at any time, without adhering to a predefined showing schedule. The subscriber is often provided VCR-like motion control functions, such as pause (freeze frame), slow motion, scan forward, and slow backward. The subscriber is typically allowed multiple views of a purchased program within a time window, e.g., 24 hours. VOD mimics (or exceeds) the level of control and convenience of rental video tapes.
Entitlement Management Messages
EMMs (Entitlement Management Messages) are control messages that convey access privileges to subscriber terminals. Unlike ECMs (Entitlement Control Messages) (discussed below) which are embedded in transport multiplexes and are broadcast to multiple subscribers, EMMs are sent unicast-addressed to each subscriber terminal. That is, an EMM is specific to a particular subscriber. In a typical implementation, an EMM contains information about the periodical key, as well as information that allows a subscriber terminal to access an ECM which is sent later. EMMs also define the tiers for each subscriber. With reference to cable services, for example, a first EMM may allow access to HBO™, ESPN™ and CNN™. A second EMM may allow access to ESPN™, TNN™ and BET™, etc.
Entitlement Control Messages
In a conditional access system, each content stream is associated with a stream of ECMs (entitlement control messages) that serve two basic functions: (1) to specify the access requirements for the associated content stream (i.e., what privileges are required for access for particular programs); and (2) to convey the information needed by subscriber terminals to compute the periodical key(s), which are needed for content decryption. ECMs are transmitted in-band alongside their associated content streams. Typically, ECMs are cryptographically protected by a “periodical key” which changes periodically, usually on a monthly basis. The monthly key is typically distributed by EMMs prior to the ECMs, as noted above.
Encryption
In a cable system, carrier signals are broadcast to a population of subscriber terminals (also known as set-top boxes). To prevent unauthorized access to service, encryption is often employed. When content is encrypted, it becomes unintelligible to persons or devices that don't possess the proper periodical key(s).
Disadvantageously, for VOD, real-time encryption poses much greater cost and space issues. A medium-sized cable system may have, for example, 50,000 subscribers. Using a common estimate of 10% peak simultaneous usage, there can be up to 5000 simultaneous VOD sessions during the peak hours. A typical encryption device can process a small number of transport multiplexes (digital carriers). Over 300 such real-time encryption devices will be needed to handle the peak usage in the example system. Such a large amount of equipment not only adds significantly to the system cost, but also poses a space requirement challenge.
One solution to the aforementioned problem is disclosed in co-pending related U.S. patent application Ser. No. 09,898,184 entitled SYSTEM FOR SECURELY DELIVERING PRE-ENCRYPTED CONTENT ON DEMAND WITH ACCESS CONTROL, filed Jul. 3, 2001, which is hereby incorporated by reference in its entirety. In U.S. patent application Ser. No. 09/898,184, a system is disclosed that encrypts content offline (typically before the content is requested by the user) before it is distributed to point-to-point systems such as cable systems. The system allows content to be encrypted once, at a centralized facility, and to be useable at different point-to-point systems. Advantageously, the pre-encrypted contents in the present invention have indefinite lifetimes. The system periodically performs an operation called ECM retrofitting, enabling the content to be useable in multiple systems and useable multiple times in the same system. The amount of data being processed during ECM retrofitting is very small (on the order of several thousand bytes). There is no need to reprocess the pre-encrypted contents. This is a significant advantage, as several thousand bytes represent only a tiny fraction of the size of a typical 2-hour video program, which is about 3 gigabytes (3,000,000,000 bytes) in size.
A first aspect of U.S. patent application Ser. No. 09/898,184 system includes a content preparation system (CPS) for pre-encrypting the content offline to form pre-encrypted content; an encryption renewal system (ERS 104) for generating entitlement control messages (ECMs) that allow the pre-encrypted content to be decryptable for a designated duration; and a conditional access system (CAS). Conventionally, the CAS controls a population of set-top boxes using a randomly generated category key. Only with possession of the category key can the pre-encrypted content be decrypted by the set-top boxes. The category key is initially forwarded to the ERS 104 which thereafter generates an ECM containing information regarding the category key. The process or requesting and generating ECMs for pre-encrypted content is known as ECM retrofitting.
After a VOD system receives pre-encrypted content and an associated encryption record, the system must receive appropriate retrofitted ECMs from the ERS 104 before the content is offered to consumers. The ECMs enable the pre-encrypted content to be decrypted. In this fashion, the ERS 104 can be connected to multiple VOD systems for which ECM retrofitting is performed. However, in order. to perform ECM retrofitting, the VOD systems must submit a request to the ERS 104. Disadvantageously, without such a mechanism, it would be relatively difficult to initiate ECM retrofitting for the pre-encrypted content. Another disadvantage of U.S. patent application Ser. No. 09/898,184, is that in some instances, each VOD server may employ a protocol version different or incompatible with the ERS 104 system version. In such cases, it necessary to employ a system allowing interoperability between all of the system components. A further disadvantage relates to the fact that ERS 104 is connectable to multiple VOD systems. Consequently, ERS 104 may become overwhelmed with multiple simultaneous requests, since the VOD systems must contact ERS 104 for the retrofitted ECMs.
Therefore, there is a need to resolve the aforementioned disadvantages and the present invention meets this need.